Beware Statistics Corruption

Robert Davis shares a story of statistics corruption causing certain queries to fail:

I suspected that there was some difference between the queries that failed and the ones that were successful in SSMS. It ran the query they gave me, and I got the same error. I got disconnected and no further error info was returned. I also verified that the same query was successful on the otehr two tables mentioned. No errors on the other tables.

I wanted to know what error was causing the connection to be terminated, so I checked the SQL log and discovered that every time it failed, it was generating a stack dump. Before I was done investigating, it had generated 21 stack dumps. The key user-usable error info in the log was:

* Exception Address = 00007FF93BCF7E08 Module(sqlmin+00000000001E7E08)
* Exception Code = c0000005 EXCEPTION_ACCESS_VIOLATION
* Access Violation occurred reading address 0000000000000000

It turns out that CHECKDB & CHECKTABLE do not look at statistics.  If you find yourself in this situation, it’s not a bad idea to see if this is the cause.

Related Posts

The Value Of Auto-Created Statistics

Brent Ozar is here to praise statistics auto-creation: Let me rephrase: before you even start playing around with statistics, make sure you haven’t taken away SQL Server’s ability to do this for you. I like to make fun of a lot of SQL Server’s built-in “auto-tuning” capabilities that do a pretty terrible job. Cost Threshold for […]

Read More

Dealing With CheckDB Error Message 824 Level 24

Steve Stedman has a post on fixing a database which has experienced an incorrect pageid error: Msg 824, Level 24, State 2, Line 1 SQL Server detected a logical consistency-based I/O error: incorrect pageid (expected 1:2806320; actual 0:0).  It occurred during a read of page (1:xxxxx) in database ID 5 at offset 0x00000xxxxx0000 in file […]

Read More

Categories

December 2015
MTWTFSS
« Nov Jan »
 123456
78910111213
14151617181920
21222324252627
28293031